Human fingerprints provide a unique and relatively economical means for identifying particular individuals. Every fingerprint typically comprises a series of spaced apart curved ridges resembling a topographical map. The ridges often form irregularities that terminate in endings and/or may split to bifurcate and form other adjacent ridges. Because of the randomness and sheer numbers of such features, data representative of the features offers a conveniently compressed form of identifier that retains the uniqueness of a full fingerprint.
Taking advantage of the uniqueness of a fingerprint's topographical characteristics, those skilled in the art have devised fingerprint identification systems to compare an unknown fingerprint to a database of known fingerprints. One such proposal, disclosed in U.S. Pat. No. 4,747,147 to Sparrow, includes a computerized fingerprint comparison system for law enforcement purposes. The system scans an unknown fingerprint and breaks down the fingerprint into predetermined minutia points comprising particular topographical characteristics. Such minutia include particular types of irregularities, the scanning angle, the ridge count, and the radial distance between minutia.
A second proposal that carries an improved version of the Sparrow teachings into the field of security systems and methods is disclosed in U.S. Pat. No. 4,947,442 to Tanaka. Tanaka implements a system having respective remote and local sites separated by transmission lines. The system extracts fingerprint data to establish predetermined minutia points from fingerprint ridge endings and bifurcations. The improvement by Tanaka includes the capability of not only detecting predetermined characteristic minutia, but also noncharacteristic minutia. This allegedly improves the resolution of detected real time fingerprints to provide a closer match between compared fingerprint files.
While the Tanaka proposal appears beneficial for its intended purposes, it suffers from a basic problem in that it cannot distinguish between a real fingerprint presented for verification, and a perfectly matching counterfeit fingerprint file injected through the transmission lines to the local site. This is because from the system's point of view, perfectly matching minutia satisfy the system's security criteria. Although such active tampering in security systems may be countered by encryption methods disposed at the remote and local sites, many operators choose not to implement such methods due to the typically prohibitive costs arising from the additional hardware and software required to effect the relatively complex encryption schemes. Moreover, other potential solutions to detect the presence of a real digit, for example blood flow or body temperature sensors, also undesirably increase hardware and software costs.
Therefore, the need exists for an economical and feasible system and method for discriminating between real fingerprints and counterfeit fingerprint data. The system and method of the present invention satisfies this need.